Generally, minerals as a metal raw material existing in a natural state are present in the form of an oxide. For example, it is known that conventionally a metal oxide such as iron, copper, nickel, cobalt, etc., can be easily reduced by hydrogen gas to extract a metal. In case of a specialty metal such as tantalum (Ta), titanium (Ti), zirconium (Zr), vanadium (V), however, conventional reduction by hydrogen gas is impossible, and thus a method for reducing a metal using an alkali metal or alkaline earth metal having strong oxidizing ability (that is, reducing ability with respect to a material to be reduced) is disclosed. An example of such method for reducing a metal has been disclosed in Korean Patent Application Publication No. 2014-0129822.
However, such alkali metal and alkaline earth metal, when in contact with an oxidizing agent such as air, generate a flame, react very explosively, and are oxidized. For example, a reducing agent such as magnesium reacts with not only air but also water or carbon dioxide to oxidize or is likely to explode. In case of the form of powder, the reactivity is very high and may affect the human body upon intake of the powder, and thus a measure to prevent it is necessary. Additionally, a method of subliming or melting by applying heat is also used in order to increase the oxidizing ability, but in this case, the explosive reaction is further accelerated, disabling its control. The conventional techniques described above are a method of controlling by introducing a material to be reduced and a reducing agent in a sealed crucible and calculating an amount of reactions and a method of controlling by charging the material to be reduced into a molten melt in which the reducing agent is melted. However, the former controlling method is based on a pre-calculated reaction amount, disabling real-time control, whereas melting condition of the reducing agent of the latter controlling method has high reactivity in most cases, thereby disabling momentary control of the molten metal temperature. Accordingly, when an unpredicted occurrence takes place during the reaction, control thereof is difficult.